Double skin composite structures

ABSTRACT

A connector which provides a joint between two double skin composite panels of a structure. Each double skin composite panel comprises a pair of metal icing plates joined together by a plurality of cross-members and filled , at least partially, with a cementitious filler material. Each cross-member is connected to both facing plates and the connector comprises one or more seamless sections.

This invention relates to double skin composite structures whichcomprise a layer of filler material (usually a cementitious materialsuch as concrete) faced with plates (usually carbon steel) and methodsof producing the same. A lighter filler material such as a filledsynthetic resin may be employed for certain applications. Moreespecially, but not exclusively, the invention concerns double skincomposite structures assembled inter alia from double skin compositepanels which comprise two facing plates positioned one on each side of alayer of concrete and connected thereto by cross members.

Double skin composite structures may be constructed from a variety ofmaterials which themselves can be used in different ways. Usually, suchstructures comprise a steel-concrete-steel sandwich construction andexhibit similar characteristics to those of reinforced concretestructures and are advantageous in that the steel facing plates act asreinforcement to enable the required strength characteristics to beachieved with structures of overall depth less than those of reinforcedconcrete. The steel facing plates also define impermeable membraneswhich protect the concrete in use. High reinforcement ratios arepossible and the steel plates act as permanent shuttering for thecentral concrete layer. The structures exhibit relatively high ductilityand impact resistance, are lighter than conventional reinforced concreteand offer reduced construction costs and decreased build times.

Double skin composite structures are known which are assembled from amultiplicity of individual double skin composite panels, each panelbeing welded to its neighbouring panels.

Thus, GB-A-2136032 and GB-A-2136033 disclose offshore structures inwhich series of arcuate elements having inner and outer steel plateslinked by steel webs and filled with cementitious material are weldedtogether. Also, GB-A-2258669 discloses a concrete-filled steel bearingwall which comprises a pair of steel surface plates secured byconnecting members and filled with concrete. Neither GB-A-2136032 norGB-A-2136033 addresses the possibility of securing, for example,horizontal and vertical elements together. GB-A-2258669 disclosesarrangements in which concrete-filled steel bearing walls supportconcrete flooring. In these arrangements, the concrete flooring simplyoverlies the upper end of the respective bearing wall to receive supporttherefrom.

It will be accepted that in all but the simplest of structures, it willbe necessary to connect sections of joined double skin composite panelstogether to form, for example, "T" and "X" joints. To do so simply bywelding together adjoining steel plates of neighbouring panels asintimated by GB-A-2136022 and GB-A-2136023 or in the manner proposed byGB-A-2258669 creates a number of problems, a major one being that someof the most critically stressed welds are inaccessible for inspectionafter the introduction of concrete between the steel plates. These weldsare also difficult to make because of poor access, tending to increasethe probability of defects which would cause problems in the structure'sservice life. Also, many of the welds are of necessity single sidedresulting in poor fatigue classification. Also for curvilinear panels,considerable material wastage may occur in cutting out the plates toform the connections.

It is an object of the present invention to provide a double skincomposite structure (and a method of producing the same) including suchjoints which overcomes, or at least alleviates, the problems discussedabove.

A "seamless section" is an elongate non-planar section produced as asingle piece to include two or more lengthwise extending elements eachof which is inclined to its neighbouring element. Seamless sections maybe produced by hot rolling, cold forming, extrusions, casting or otherforming process. The angle between neighbouring elements may be a rightangle or an angle below 90° or above 90°. Sections include "I" sections,"H" sections, "T" sections, channel sections, angled sections, andhollow sections. An important feature of a seamless section is thatwhere neighbouring elements meet a radiussed transition of solid metalis formed.

By the term "double skin composite panel" is meant a panel whichcomprises two substantially parallel facing plates joined together by aplurality of connecting members disposed generally normal to the facingplates in a plurality of spaced rows with each connecting member securedto one or both facing plates, the panel interior being subsequentlyfilled with a filler material, e.g. a cementitious material.

According to the present invention in one aspect, there is provided adouble skin composite structure in which neighbouring double skincomposite panels of the structure are connected by welding to aconnector fabricated from one or more non-planar seamless sections.

In another aspect, the invention provides a connector for providing ajoint between two double skin composite panels to produce a structure,each such double skin composite panel comprising a pair of metal facingplates joined together by a plurality of cross-members and filled, atleast partially, with a filler material, each such cross-member beingsecured to one or both facing plates and the connector comprising atleast one non-planar seamless section having protruding flanges to whichthe edges of the facing plates of one double skin panel are welded.

In a further aspect, the invention provides a structure comprising afirst generally horizontal double skin composite panel and a secondgenerally vertical double skin composite panel, each panel comprisingtwo metal facing plates joined together by a plurality of transversecross-members and filled with a cementitious material and a connectorfor joining the panels together, the connector comprising a plurality ofnon-planar sections welded together to define a hollow section to whichthe facing plates of the respective panels are welded.

The invention will now be described by way of example with reference tothe accompanying diagrammatic drawings in which:

FIG. 1 is a side view in section of a double skin composite structure inaccordance with the invention;

FIGS. 2 and 3 are side or plan views in section of alternative doubleskin composite structures in accordance with the invention;

FIGS. 4 and 5 diagrammatically illustrate the assembly of a double skincomposite structure in accordance with the invention; and

FIG. 6 is a perspective view of a double skin composite structure inaccordance with the invention after assembly.

The structure illustrated in FIG. 1 comprises a horizontal double skincomposite structure prefabricated by welding together a generallyhorizontal prefabricated double skin composite panel and two verticaldouble skin composite panels 2, 3. Each double skin composite panelcomprises a pair of generally parallel steel facing plates 4 joinedtogether by a plurality of transverse metal crossmembers members 5 eachwelded at each of its ends to the adjoining facing plate. The spacingbetween the facing plates is subsequently filled with a filler material,conventionally concrete.

The fabricated panels 1, 2, 3 are joined by a connector 6 prefabricatedfrom two non-planar seamless sections in the form of hot rolled steelsections 7, 8 secured together by welds 9 to define a hollow section 10from which protrude upwardly extending flanges 11 and downwardlyextending flanges 12.

It has been established that forces and hence stresses in double skincomposite structures tend to concentrate at the sites of the connectionsbetween the joined panels and the use of non-planar seamless sectionssuch as hot-rolled sections (as opposed to sections produced simply bywelding a web to one or more flanges) has been found to be highlyadvantageous. This is firstly because local increases in plate thicknessat the interconnections between the webs and the flanges produced by hotrolling provides added strength which counteracts and reduces stressconcentrations. Secondly, the radius produced by hot rolling at theinterconnections between the webs and flanges ensures that forces flowbetween the joined structures again reducing stress concentrations andextending fatigue life. A further advantage is that hot rolled sectionscan readily be bent to a radius thereby enabling their use in both flatand curved constructions.

Before assembly of the prefabricated panels, panel 3 is filled withconcrete to the level indicated by reference numeral 14. The hollowsection 10 of the connector 6 is then welded to the facing plates 4 ofthe respective end of the horizontal panel 1 along welds 15 between theabutting edges of the facing plates of the panel 1 and the outer face ofthe hollow section 10 defined by hot rolled sections 7, 8. Generally thefacing plates will be arranged to line up with the web of any sectionmaking up the connector. Panel 1 and the attached connector 6 is thenassembled onto the panel 3 by making welds 16 between the edges of thedownwardly extending flanges 12 of the lower hot rolled section 8 andthe steel facing plates of the lower vertical prefabricated panel 3.

As will be seen from FIGS. 4 and 5, guides 17 may be attached to theinternal surfaces of the flanges 12 of the hot rolled section 8 toassist accurate assembly. Alternatively, the guides 17 may be attachedto the internal surfaces of the facing plates of panels 2 and 3. Theguides 17 are inwardly inclined and may be formed with openings for theflow of cement therethrough.

In addition to assisting accurate assembly, the guides 17 can be used asbacking plates for welds made between the structures following assembly.

At the appropriate time, the upper vertical prefabricated panel 2 ispositioned on the upstanding flanges 11 of the upper hot rolled section7. The facing plates of panel 2 are then welded to the adjoining flanges11. Concrete is subsequently introduced into the prefabricated panel tofill the same. Alternatively, the concrete may be pumped into the voidabove reference line 14, holes being provided in the flanges of the hotrolled sections 7, 8 to allow the concrete to fill the voids and theprefabricated panel 2.

As shown in FIG. 5, a panel 18 is subsequently welded to one side of theconnector between the composite structures. This panel 18 may beinclined as illustrated or lie substantially horizontal.

In the construction illustrated in FIG. 2, the connector between thepre-fabricated horizontal and vertical panels is fabricated by weldingtogether a channel-shaped hot rolled section 21 and a hot rolled "I"section 22. In the construction illustrated in FIG. 3, a single steelsheet 19 is welded to one side face of an "I" seamless section 20.Assembly of the structures is similar to that described above. Theconstructions illustrated in FIGS. 1 and 2 of the drawings are merelyexemplary of many constructions which can be employed in accordance withthe invention.

An assembled joined structure is illustrated in FIG. 6. It will be seenthat the hot rolled connector 23 and the joined double skin compositevertical panels 24, 25 are curvilinear with the adjoining edge of thehorizontal panel 26 suitably shaped to complement the curved face of theconnector 23. Holes 27 are formed in the connector 23 for the flow offiller material.

It will be appreciated from the foregoing that by using hot rolledsections in accordance with the invention, the number of welds which areinaccessible is minimised, only one of the welds of the constructionillustrated in FIG. 1 being entirely inaccessible once concrete has beenintroduced into the prefabricated sections. This weld is located in therelatively thicker, and hence lower stressed, flange of the connectorand is unlikely to be of concern. Also, with the constructionillustrated, stresses which tend to be concentrated at the connector canreadily be offset by using hot rolled sections which result in localincreases in face plate thickness. This thickening acts generally toreduce stresses in critical regions. Furthermore, hot rolled sectionshave radii where the web and flanges interconnect; these radii helpforces to flow from one structure to another thereby reducing stressconcentrations and extending fatigue life.

As mentioned above, hot rolled sections can be bent to a radius, therebyenabling their use in both flat and curved constructions, greatly savingon fabrication effort.

It will be appreciated that the foregoing is merely Exemplary ofstructures in accordance with the invention and that modifications canreadily be made thereto without departing from the true scope of theinvention as set out in the appended claims.

We claim:
 1. A double skin composite structure in which neighbouringdouble skin composite panels of the structure are connected by welding,the structure being characterised in that the composite panels arewelded to a connector fabricated from one or more non-planar seamlesssections, the or each seamless section being produced as a single pieceand including two or more lengthwise extending elements each of which isinclined to its neighbouring element.
 2. A structure as claimed in claim1 in which the connector is fabricated from two non-planar seamlesssections secured together by welds to define hollow section from whichprotrude flanges to which edges of facing plates of an adjoining panelare secured.
 3. A structure as claimed in claim 1 in which the or eachnon-planar seamless section is a hot rolled section.
 4. A structure asclaimed in claim 1 in which the or each non-planar seamless section isan extruded section.
 5. A structure as claimed in claim 1 in which theor each non-planar seamless section is a cold formed section.
 6. Astructure as claimed in claim 1 in which the or each non-planar seamlesssection is a cast section.
 7. A structure as claimed in claim 1 whereinguides are secured to internal surfaces of flanges which protrude fromthe connector, the guides being positioned such that they align withinternal surfaces of an adjoining panel to assist assembly.
 8. Aconnector which defines a joint between two doubled skin compositepanels to produce a structure, each such double skin composite panelcomprising a pair of metal facing plates joined together by a pluralityof cross-members and filled, at least partially, with a filler material,and each such cross-member being connected to one or both facing plates,the connector comprising at least one non-planar seamless section havingprotruding flanges to which edges of the facing plates of one doubleskin panel are welded, the or each seamless section being produced as asingle piece and including two or more lengthwise extending elementseach of which is inclined to its neighbouring element.
 9. A connector asclaimed in claim 8 which comprises a plurality of non-planar seamlesssections welded together to define a box section with protruding flangesto the edges of which the facing plates of one double skin panel arewelded, the facing plates of the other double skin panel being welded toone side of the box section.
 10. A connector as claimed in claim 8wherein one panel is disposed at an angle of or approaching 90° to theother panel.
 11. A connector as claimed in claim 8 wherein guides aresecured to internal surfaces of the protruding flanges to assistalignment of the connector and an adjoining panel to be welded thereto.12. A structure comprising a first generally horizontal double skincomposite panel and a second generally vertical double skin compositepanel, each panel comprising two metal facing plates joined together bya plurality of transverse metal cross-members and filled with acementitious material and a connector joining the panels together, theconnector comprising a plurality of non-planar seamless sections weldedtogether to define a hollow section having protruding flanges to whichthe facing plates of the respective panels are welded.
 13. A connectoras claimed in claim 8 wherein holes are formed in one or more connectorsurfaces for through flow of filler material.